Signal navigation and label propagation in block diagrams

ABSTRACT

A system and method that includes line connection navigation in a block diagram by highlighting connections through navigable blocks in the diagram, edit-time label propagation along connections and through navigable blocks that can propagate labels through their ports, API to define navigability between block ports, and displaying implied connections between blocks.

TECHNICAL FIELD

[0001] The present invention relates to signal navigation and label propagation in block diagrams.

BACKGROUND

[0002] Various classes of block diagrams describe computations that can be performed on application specific computational hardware, such as a computer, microcontroller, FPGA, and custom hardware. Classes of such block diagrams include time-based block diagrams such as those found within Simulink® from the MathWorks, Inc. Natick Mass., state-based and flow diagrams such as those found within Stateflow® from the MathWorks, Inc. Natick, Mass., and data-flow diagrams. A common characteristic among these various forms of block diagrams is that they define semantics on how to execute the diagram.

SUMMARY

[0003] In an aspect, the invention features a method including, in a block diagram model, tracing a signal connection through navigable blocks.

[0004] One or more of the following features can also be included. Tracing can be in response to a user request. Tracing can include displaying tracing results on a graphical user interface (GUI). Displaying can include highlighting the signal connection on the GUI. Displaying can include displaying implied signal connections on the GUI.

[0005] In embodiments, tracing can include providing an application program interface (API) for block in the block diagram model to specify how navigation occurs between inputs and outputs. The API further can include specification of how navigation occurs between the outputs and the inputs.

[0006] In another aspect, the invention features a method including in a block diagram edit-phase, propagating a signal label through navigable blocks.

[0007] One or more of the following features can also be included. Propagating can be in response to a user input. Propagating can include displaying the propagated signal label on a graphical user interface (GUI). Displaying can include showing signal labels on implied signal connections on the GUI.

[0008] In embodiments, tracing can include providing an application program interface (API) for block in the block diagram model to specify how navigation occurs between inputs and outputs. The API can include specification of how navigation occurs between the outputs and the inputs.

[0009] In another aspect, the invention features a method including in a block diagram model, displaying an implied signal connection.

[0010] One or more of the following features can also be included. Displaying can be in response to a user activating a hyperlink provided on a block that has an implicit signal connection with another block. Displaying can be in response to a user activating a hyperlink on a dialog of a block that has an implicit signal connection with another block.

[0011] Displaying can include highlighting blocks involved in the implied signal connection. Displaying can include automatically drawing lines between blocks that have implied signal connections.

[0012] In another aspect, the invention features a Graphical User Interface (GUI) for displaying results from a signal navigation including a first element that defines a highlighting contrast value for determining a contrast between a highlighted portion and a remainder of a block diagram model, and a second element that highlights non-navigable source blocks and non-navigable destination blocks.

[0013] One or more of the following features can also be included. The first element can include a command to enable a user to change the contrast. The first element can include a dialog box to enable a user to change the contrast.

[0014] In embodiments, the GUI can include a third element that highlights an entire signal path from its non-navigable source to its non-navigable destination, a fourth element that fades a remainder of the block diagram model so that a highlighted portion is easily identified, and/or a fifth element that enables a user to de-emphasize portions of the block diagram that are not highlighted.

[0015] The details of one or more embodiments of the invention are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the invention will be apparent from the description and drawings, and from the claims.

DESCRIPTION OF DRAWINGS

[0016]FIG. 1 is a block diagram of a system.

[0017]FIG. 2 is a first block diagram model.

[0018]FIG. 3 is a connectivity graph of the block diagram model of FIG. 2.

[0019]FIG. 4 is a flow diagram of a block diagram modeling process.

[0020]FIG. 5 is a flow diagram of a signal non-navigable destination tracing function.

[0021]FIG. 6 is a flow diagram of a signal non-navigable destination tracing function.

[0022]FIG. 7 is a graphical user interface (GUI).

[0023]FIG. 8 is a GUI.

[0024]FIG. 9 is a GUI.

[0025]FIG. 10 is a GUI.

[0026]FIG. 11 is a GUI.

[0027]FIG. 12 is a GUI.

[0028]FIG. 13 is a GUI.

[0029]FIG. 14 is a GUI.

[0030]FIG. 15 is a GUI.

[0031]FIG. 16 is a GUI.

[0032]FIG. 17 is a GUI.

[0033]FIG. 18 is a GUI.

DETAILED DESCRIPTION

[0034] In FIG. 1, a system 10 includes a processor 12 and a memory 14. Memory 14 stores an operating system (“O/S”) 16 such as Linux or Microsoft Windows XP, a TCP/IP protocol stack 18 for communicating over a network (not shown), and machine-executable instructions 20 executed by processor 12 to perform a block diagram modeling process 100 below. System 10 also includes a storage device 22 and an input/output (“I/O”) device 24. The I/O device 24 can include a graphical user interface (“GUI”) 26 for display of a block diagram model to a user 26.

[0035] An example block-diagram modeling process 100 is Simulink from The Mathworks, Inc. of Natick, Mass. Other examples of block diagram modeling processes include state-based and flow diagrams such as those found within Stateflow from The Mathworks, Inc. of Natick, Mass., data-flow diagrams, etc.

[0036] To illustrate the concepts of this invention, we will focus on time-based block diagrams such as those found in Simulink. Those skilled in the art will recognize that these concepts apply to other block diagram models of computation. Time-based block-diagram modeling simplifies the process of conceptualizing, designing, simulating, and implementing (in software or hardware) dynamic systems. These block-diagrams models define time-based relationships between signals (represented as lines on the block diagram) and state variables representative of a dynamic system. The solution (computation of system response) of the model is obtained by evaluating these relationships over time, where time starts at a user-specified “start time” and ends at a user-specified “stop time”. Each evaluation of these relationships is referred to as a time step. Signals represent quantities that change over time, and these quantities are defined for all points in time between the block-diagram's start and stop time. The relationships between signals and state variables are defined by sets of equations represented by blocks. These equations define a relationship between the input signals, output signals, and state variables. Inherent in the definition is the notion of parameters, which are the coefficients of the equations.

[0037] Using time-based block-diagram software, such as Simulink, for modeling, simulating, and analyzing a dynamic system typically involves two major phases: edit and execute. In the edit phase, users add or remove blocks to/from the block-diagram model and connect blocks using lines. In particular, users add two categories of blocks: virtual and non-virtual blocks. Virtual blocks do not influence the mathematical model of the dynamic system and are for improving modularity and readability of the block-diagram. Non-virtual blocks directly influence the mathematical equations for the dynamic system. In the execution phase, the model is used to compute and trace the corresponding dynamic system's outputs. During one of the preliminary steps of the execution phase known as the compile stage, virtual blocks are eliminated from the block-diagram and a connectivity graph including only non-virtual blocks is generated.

[0038] Examples of virtual blocks are as follows. (a) Virtual subsystems: Modularity is sometimes achieved in a block-diagram by layering the block-diagram through the use of subsystems. A subsystem facilitates layering by allowing a collection of blocks to be represented by a single block with input and output signals. The input and output signals of the subsystem are accessible to the constituent blocks within the Subsystem. A subsystem is virtual if its constituent blocks are moved back into the main block-diagram model during the model's execution. (b) Inports and Outports: Within a virtual subsystem, there needs to be a graphical entity that serves to indicate the signal connections to the parent block-diagram. These entities are special inport and outport blocks that indicate a tunnel-through signal connection to the parent block-diagram. (c) Bus Creators and Selectors: In large models, there may be an extensive set of lines that connect one section of a block-diagram to another section. To avoid excessive clutter of lines and improve readability, there is typically a special block called a Bus Creator that helps bundle all of the lines together to form a single bus line. This single bus line then connects the two sections of the model. At the destination end of the line, a block called a Bus Selector helps un-bundle the individual lines so that they can be connected to other blocks. (d) Froms and Gotos: These are special blocks that help avoid graphical clutter caused by a line that connects two distant sections of a block-diagram. The line is terminated close to its originating point by a From block. At the other end, a new line is drawn from a Goto block that is hot-linked to the From block.

[0039] The virtual blocks are one form of navigable blocks where a signal can be traced from input to output and vice versa. Non-virtual blocks could be either navigable or non-navigable. Non-navigable non-virtual blocks do not permit a signal to be traced form input to output, or vice versa. An example of a navigable non-virtual block is the unit delay for which the signal can be traced directly from input to output port. Lines in the block diagram can be labeled to indicate a symbolic name for the signal represented by the line. To aid in tracability of a signal, it is important to be able to be able to propagate and display a unique label on a signal line while it is being traced through various navigable blocks.

[0040] In the current state of the art, the tracing and navigation of signals through navigable blocks must be done manually and label propagation is done during block diagram compilation. Once the connectivity graph is made available during block-diagram compilation, it becomes possible to navigate the block-diagram to trace and highlight signals and to propagate labels through all navigable blocks. But, during the edit phase, when the connectivity graph is unavailable, in prior art there are no mechanisms to allow users to navigate through navigable blocks. Furthermore, in prior art, there was no mechanism for marking non-virtual blocks as being navigable.

[0041] In FIG. 2, an exemplary block diagram model 40 includes a sine wave block 42, a constant block 44, a bus creator block 46, a bus selector block 48, a scope block 50 and a scope block 52. The model 40 also includes a signal 54. The signal 54 is a bus that represents a bundle of signals analogous to a bundle of wires held together by tie wraps. Bus creator block 46 and bus selector block 48 are virtual blocks. Sine wave block 42, constant block 44, scope block 50 and scope block 52 are non-virtual blocks. The signal line between the bus creator block 46 and bus selector block 48 is the signal bus 54.

[0042] In FIG. 3, a corresponding connectivity graph 56 of FIG. 2, where the bus selector block 48 and bus creator block 46 are removed, is shown. As discussed above, when the connectivity graph 56 is formed from the model 40 in the block-diagram compile phase, all the virtual blocks are removed. Thus, the connectivity graph 56 does not include the virtual blocks 46, 48, 54. The connectivity graph 56 includes a signal line 58 connecting the sine wave block 42 to the scope block 50 and a signal line 60 connecting the constant block 44 to the scope block 52.

[0043] Each signal in a block-diagram can have a name. A label on the corresponding line displays the signal's name. A signal retains its name (or label) when a signal connection can be traced through a navigable block. That is, the label is propagated through all navigable blocks. For example, a name of an output signal of the sine wave block 42 is “a,” an input signal of the scope block 50 is connected to signal “a” via the bus creator 46 and the bus selector block 48. These two lines represent the same signal. The signal label “<a>” shown on the input line to the scope block 50 is a propagated signal label. In Simulink®, propagated signal labels are enclosed by angle brackets (“

”).

[0044] A non-navigable block's output port that generates a signal is referred to as a non-navigable source of the signal. A signal bus can have multiple non-navigable sources. A non-navigable block's input port that reads a signal is referred to as a non-navigable destination of the signal. One signal can have multiple non-navigable destinations. For example, sine wave block 42 is a non-navigable source of the signal “a”, and the scope block 50 is a non-navigable destination of the signal “a”.

[0045] Tasks of signal navigation in a block-diagram include: (1) tracing and highlighting a non-navigable source and non-navigable destination(s) of a signal line; (2) propagating signal labels from a signal's non-navigable source through navigable blocks; (3) displaying connections that are implied by navigable blocks that are implicitly connected to each other; and (4) providing an interface for blocks to specify their navigability properties.

[0046] When users are generating block-diagrams to simulate a real-world system, an ability to navigate signals through navigable blocks is needed. This need to navigate is particularly true for large and complex block-diagrams, where a large number of signals can cross multiple layers of the block diagram. In such examples, navigable blocks, such as bus creator block 46 and bus selector block 48 are frequently used for better organizing graphical connections of signals.

[0047] In the past, block-diagram software relied on the connectivity graph of a block-diagram for signal navigation, such as signal label propagation. There are a number of limitations of this type of signal navigation process. For example, because the connectivity graph is only generated in the block-diagram compile phase, users are not able to view propagated signal labels, trace non-navigable source and destination(s) of a signal, and highlight a signal connection in the block-diagram, until the block-diagram is compiled and the corresponding connectivity graph is obtained. This limitation prevents users from getting enough graphical feedback, such as viewing propagated signal labels, while editing a block-diagram. Such graphical feedback at the block-diagram edit time is often crucial for detecting a modeling error at an early stage. The computational resources, e.g., time and memory, associated with compilation for a large block-diagram that may contain 1000+ blocks are typically expensive. Users have to wait until the block-diagram compilation is finished to be able to view propagated signal labels and locate non-navigable source and destination(s) of a signal. Thus, in traditional signal navigation mechanism users have to alternate between the block-diagram edit and compile phases. This process is time-consuming. Also, there is no support for specifying the navigability properties of non-virtual blocks.

[0048] For another example, because the connectivity graph does not contain any virtual blocks, a one-to-one mapping between the nodes in the connectivity graph and the nodes in the graphical block-diagram generated by a user typically do not exist. The traditional signal navigation process relying on compiled graph connectivity information prevents the user from highlighting a complete signal connection from the signal's non-navigable source through all intermediate navigable blocks to its non-navigable destinations, because in the compile phase, virtual blocks have been removed from the connectivity graph.

[0049] In FIG. 4, the block diagram modeling process 100 includes an editing stage (102) and an execution stage (106). In contrast to traditional signal navigation, the block diagram modeling process 100 includes an edit-time signal navigation process 200 that enables users to navigate signals in a block-diagram through navigable blocks in the editing process (102). When a user is editing a block-diagram, a changed signal label is propagated instantly through navigable blocks without having to execute a compilation process (104). The user is also provided an ability to trace a non-navigable source or destination(s) of any signal in the block-diagram at edit time (102). In addition, the user can highlight a signal connection through navigable blocks. With these edit-time signal navigation abilities, users are given instantaneous graphical feedback on the block-diagrams being edited. The edit-time signal navigation process 200 can shorten the time for developing a block diagram model.

[0050] The edit-time signal navigation process 200 provides a signal navigation ability at block-diagram edit stage (102). The edit-time signal navigation process 200 does not rely on any information obtained in the block-diagram compile phase (104). The edit-time signal navigation process 200 includes a set of signal navigation functions (202).

[0051] A first signal navigation function provided by the edit-time signal navigation process 200 is instantaneous signal label propagation through navigable blocks. When users change a signal's label in the block-diagram via the GUI 26, a user interface such as mouse or keyboard, or programmatically, the changed signal label is instantly propagated to all the signal lines connected through navigable blocks.

[0052] A second signal navigation function provided by the edit-time signal navigation process 200 is tracing a signal's non-navigable source and destination(s) from a line. At block-diagram edit time (102), users can request tracing of a signal's non-navigable source or destination(s) from the line that represents the signal. For example, users can right click on a signal line and choose “highlight to source” or “highlight to destination” to trace a signal to its non-navigable source or destination. Alternatively, they may use a user interface such as a keyboard or a programmatic application program interface (API) to request the tracing capability. The second function also highlights the signal connection through navigable blocks. Users can also invoke this function through commands on other user interfaces such as a keyboard or mouse. Additionally, users could invoke this function through the use of a programmatic interface.

[0053] A third function provided by the edit-time signal navigation process 200 is tracing signal connections that are implied through implicit block connections. For example, there is an implicit connection between a Goto block and all corresponding From blocks. These implicit connections can be shown on the GUI 26 through an explicitly drawn signal line.

[0054] A fourth function provided by the edit-time signal navigation process 200 is providing an interface for each type of block to be able to specify its specific navigability properties. For example, users can utilize this interface to specify the exact navigability property of a custom block that they have defined.

[0055] An example of a block navigability interface provided by edit-time signal navigation process 200 is what we refer to as “walkthrough functions for navigable blocks.” When a signal is connected to a navigable block's input port, the navigable block knows which output port the signal is effectively connected to. Therefore, the edit-time signal navigation process 200 introduces walk-through for every navigable block, i.e. a walk-through method of a navigable block determines the signal connection across the navigable block. In particular, every navigable block has two walk-through methods, one to its source direction, and the other to its destination direction.

[0056] The edit-time signal navigation process 200 includes Graphical User Interfaces (GUIs) for displaying non-navigable source/destination(s) and a signal connection. When users work on complex block-diagrams, it is often difficult to track a signal connection visually. Therefore, it is necessary to make the signal connection and the identified non-navigable source or destination(s) stand out from the rest of the block-diagram.

[0057] The edit-time signal navigation process 200 implements a GUI representation for visually displaying results from signal navigation. The GUI representation for visually displaying results from signal navigation can include one or more of the following four elements.

[0058] A first element of the GUI representation defines a highlighting contrast value for determining the contrast between the highlighted portion and the remainder of a block-diagram. The first element can also include a command (or a GUI) for users to change this contrast value to their preferable number.

[0059] A second element of the GUI representation highlights the non-navigable source or destination blocks.

[0060] A third element of the GUI representation highlights the entire signal connection from its non-navigable source to non-navigable destination(s).

[0061] A fourth element of the GUI representation fades the remainder of the block-diagram so that the highlighted portion is easy to identify.

[0062] In an example, highlighting and fading are combined in the GUI representation such that not only is the users' attention attracted to the highlighted portion, but the GUI representation also de-emphasizes the remainder of the block-diagram and removes distractions for the user. The highlighting and fading can be extended to other examples that use GUI representation for highlighting objects.

[0063] The edit-time signal navigation process 200 includes inputs and outputs for edit-time label propagation. Inputs include a block diagram containing blocks interconnected by lines, a signal line whose label is being edited in the block diagram model, and a signal's new label and old label. Outputs include signal labels of all the lines that can be propagated to/from the signal line whose name is being edited and display the propagated signal labels to these lines.

[0064] The edit-time signal navigation process 200 includes inputs and outputs for edit-time signal non-navigable source and destination(s) tracing from a line. Inputs include a block diagram containing blocks interconnected by lines and a signal line being selected for tracing its source or destination(s). Outputs include highlighted non-navigable source or destination(s) block and highlighted signal connection from the selected line to its source or destination direction or both.

[0065] The edit-time signal navigation process 200 includes inputs and outputs for tracing implied connections between implicitly connected blocks. Inputs include a block-diagram containing blocks, including implicitly connected blocks, interconnected by lines and a selected block with an implicit connection. Output includes either a textual or a highlighted display of the implicit connection and the block(s) connected to the selected block.

[0066] In general, a data structure can be used to represent a signal line(s) as: class SignalLine {   private:     String label;     OutputPort source;     int numDestinations;     InputPort *destinations;   public:     <Methods for Signal class> };

[0067] We now describe processes for tracing the non-navigable source and destination(s) of a signal line. We first present an overview of walk-through functions and their implementations for some common navigable blocks. Finally, we use flow-diagrams to describe how walk-through functions may be used to trace the non-navigable source and destination(s) of a signal line.

[0068] Each block data-structure can be considered to implement a pair of walk-through functions that operate on the block. There are two kinds of walk-through functions, i.e., walk-through to source direction and walk-through to destination direction, for every block. Both walk-through functions receive two incoming arguments and two outgoing arguments. For walking through to source direction, we pass the block's output port index (outputPortIndex) and the selected line's graphical destination input port (origInputPort) into the block's WalkThroughToSourceDirection function, and this function returns the number of input ports (*num) it can walk through to and an array of such input ports (*inputPorts). For walking through to destination direction, we pass the block's input port index (inputPortIndex) and the selected line's graphical source port (origOutputPort) into the block's WalkThroughToDestinationDirection function, and this function returns the number of output ports (*num) it can walk through and an array of such output ports (*outputPorts). A possible implementation is as follows:      class Block {          private:              <Block data fields>              <Block private methods>          public:              <Other block methods>              WalkThroughToSourceDirection (int outputPortIndex,                  InputPort origInputPort,                  int *num,                  InputPort *inputPorts);              WalkThroughToDestinationDirection (int      inputPortIndex,                  OutputPort origOutputPort,                  int *num,                  OutputPort   *outputPorts); };

[0069] For example, we describe the walk-through functions for a non-virtual block, “From”, “Goto”, “Bus Creator” and “Bus Selector” blocks as follows:

[0070] For a non-navigable non-virtual block, both walk-through functions return number of ports (num) they can walk to as 0. They also return empty for the port indices (inputPortIndices or outputPortIndices). However, the system can also explicitly specify walk-through functions for non-virtual blocks as desired. The Goto block's WalkThroughToDestinationDirection function returns num to be equal to the number of From blocks driven by the Goto block. The function also returns the output ports of all of the From blocks (in outputPorts).

[0071] The From block's WalkThroughToSourceDirection function returns num to be equal to 1 because there is exactly one Goto block driving the From block. The function also returns the input port of the Goto blocks (in inputPorts).

[0072] The Bus Selector block's WalkThroughToDestinationDirection function first checks the structure of the signal connected to origOutputPort to see if it is a bus. If the signal is not a bus, then the block checks each of its output ports to determine which output port signal corresponds to the signal connected to origOutputPort. This port is returned in outputPorts. If the signal connected to origOutputPort is a bus, then the block checks each of its output ports to see if any signal in the bus is part of the output port signal. All ports that correspond to signals in the bus connected to origOutputPort are returned in outputPorts.

[0073] The Bus Creator's WalkThroughToSourceDirection function first checks the structure of the signal connected to origInputPort to see if it is a bus. If the signal is not a bus, then the block checks each of its input ports to determine which input port signal corresponds to the signal connected to origInputPort. This port is returned in inputPorts. If the signal connected to origInputPort is a bus, then the block checks each of its input ports to see if any signal in the bus is part of the input port signal. All ports that correspond to signals in the bus connected to origInputPort are returned in inputPorts.

[0074] Similar functions can be defined on Inports, Outports, and Virtual Subsystems to help with walk through.

[0075] In FIG. 5, a signal non-navigable source tracing function 400 TraceSource (Line line, InputPort orig_port) is shown. The function 400 receives two parameters, i.e., line 402 and input port 404 and uses walk through recursively to trace back to the non-navigable source of a signal.

[0076] In FIG. 6, a signal non-navigable destination tracing function 450 TraceDestination (Line line, OutputPort orig_port) is shown. The function 450 receives two parameters, i.e., line 452 and output port 454 and uses walk through recursively to trace back to non-navigable destination of a signal.

[0077] An edit-time signal label propagation process is similar to the non-navigable destination tracing process described above. A SignalLabelProp function (Line line, OutputPort orig_port, String new-label, String old-label) accepts four arguments. First, the line where the signal label changes. Second, the graphical source port of the line. Third, the new signal label. Fourth, the old signal label. This function starts from the line where the signal label changes and visits all the signal lines connected by navigable blocks like the functions TraceSource and TraceDestination. For each visited signal line, update its signal label, i.e. replace old-label with new-label. In Simulink®, a bus selector block determines which input signal is connected to which output signal by matching signal labels. When an input bus selector block is encountered, some additional care is needed. In the selected signals, we replace old-label with new-label, thus the signal connection remains unchanged, although signal label is updated.

[0078] In FIG. 7, a Graphical User Interface (GUI) 500 is shown for non-navigable source and destination(s) tracing. A signal line “a” 502 is selected, the right click context menu 504 has two highlighting items: “Highlight to source” 506 and “Highlight to destination” 508, which are used to trace the non-navigable source and destination(s) of the signal “a”, respectively.

[0079] In FIG. 8, a GUI 520 is shown. Tracing the non-navigable destination of the signal line “a” 522, which is “Out3” block 524. The GUI 520 shows three things. First, the full signal connection from “Constant1” block 526 (non-navigable source) to “Out3” (non-navigable destination) block 524 is highlighted. Second, the non-navigable destination block is highlighted with shaded background and shaded foreground colors. Third, the remainder of the block-diagram fades so that the highlighted portion stands out.

[0080] In FIG. 9, a GUI 540 is shown. Setting the highlighting contrast to its maximum value, tracing the non-navigable destination of a signal line. The remainder of the model vanishes.

[0081] In FIG. 10, a GUI 560 is shown. Tracing the non-navigable source of the signal coming into the input port of the “Out5” block 562. The full signal connection through navigable blocks (“Bus Creator” 564 and “Bus Selector” 566 blocks) is highlighted. The non-navigable source block, which is the “Constant2” block 568 is highlighted with shaded background and shaded foreground colors.

[0082] In FIG. 11, a GUI 580 is shown. Tracing the non-navigable source of the signal labeled as “a” from the “Bus Creator” block 582. Select “a” from the dialog box 584 of the “Bus Creator” block 582, and press “Find” button 586, the non-navigable source block of the signal “a” is highlighted. Multiple signals can be selected and highlighted, e.g. “a”, “b”, “c” can be selected simultaneously, then press “Find” button 586, three non-navigable sources are highlighted.

[0083] In FIG. 12, a GUI 600 is shown. Tracing the corresponding “Goto” block 602 from a “From” block 604. Open the dialog box 606 of the “From” block 604, double click on the line next to the “Goto source” label 606, the corresponding “Goto” block 602, which is “Goto1” in this example, is highlighted. This is an example of tracing implicit signal connections.

[0084] In FIG. 13, a GUI 620 is shown. Tracing the corresponding “From” block 622 from a “Goto” block 624. In this example, open the dialog box 626 of the “Goto1” block 624, there are three “From” blocks derived from this “Goto” block. Double clicking on the name of a “From” block will highlight the corresponding “From” block. Multiple “From” blocks can be traced simultaneously by selecting multiple “From” blocks from the dialog box 626. This is an example of tracing implicit signal connections.

[0085] In FIG. 14, a GUI 640 shows the original block-diagram for edit-time signal label propagation example, described above.

[0086] In FIG. 15, a GUI 660 includes the dialog box of the “Bus Selector” block in FIG. 14. The input signals include “a”, “b” and “c” as shown on the left side. The selected signals include “a” and “b” as shown on the right side.

[0087] In FIG. 16, a GUI 680 includes changing the signal label 682 “a” to “N”.

[0088] In FIG. 17, a GUI 700 shows that as soon as the signal label 702 is changed, the new label “N” is propagated through navigable blocks, i.e. “Goto” 704, “From” 706, “Bus Creator” 708 and “Bus Selector” 710 blocks.

[0089] In FIG. 18, a GUI 720 shows when the new signal label “N” is propagated to the “Bus Selector” block, the “Bus Selector” block automatically updates “a” to “N” in selected signal column.

[0090] The invention can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The invention can be implemented as a computer program product, i.e., a computer program tangibly embodied in an information carrier, e.g., in a machine-readable storage device or in a propagated signal, for execution by, or to control the operation of, data processing apparatus, e.g., a programmable processor, a computer, or multiple computers. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment. A computer program can be deployed to be executed on one computer or on multiple computers at one site or distributed across multiple sites and interconnected by a communication network.

[0091] Method steps of the invention can be performed by one or more programmable processors executing a computer program to perform functions of the invention by operating on input data and generating output. Method steps can also be performed by, and apparatus of the invention can be implemented as, special purpose logic circuitry, e.g., an FPGA (field programmable gate array) or an ASIC (application-specific integrated circuit).

[0092] Processors suitable for the execution of a computer program include, by way of example, both general and special purpose microprocessors, and any one or more processors of any kind of digital computer. Generally, a processor will receive instructions and data from a read-only memory or a random access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memory devices for storing instructions and data. Generally, a computer will also include, or be operatively coupled to receive data from or transfer data to, or both, one or more mass storage devices for storing data, e.g., magnetic, magneto-optical disks, or optical disks. Information carriers suitable for embodying computer program instructions and data include all forms of non-volatile memory, including by way of example semiconductor memory devices, e.g., EPROM, EEPROM, and flash memory devices; magnetic disks, e.g., internal hard disks or removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in special purpose logic circuitry.

[0093] The invention has been described in terms of particular embodiments. Other embodiments are within the scope of the following claims. For example, the steps of the invention can be performed in a different order and still achieve desirable results. Accordingly, other embodiments are within the scope of the following claims. 

What is claimed is:
 1. A method comprising: in a block diagram model, tracing a signal connection through navigable blocks.
 2. The method of claim 1 in which tracing is in response to a user request.
 3. The method of claim 1 in which tracing comprises displaying tracing results on a graphical user interface (GUI).
 4. The method of claim 3 in which displaying further comprises highlighting the signal connection on the GUI.
 5. The method of claim 3 in which displaying further comprises displaying implied signal connections on the GUI.
 6. The method of claim 1 in which tracing comprises providing an application program interface (API) for block in the block diagram model to specify how navigation occurs between inputs and outputs.
 7. The method of claim 6 in which the API further comprises specification of how navigation occurs between the outputs and the inputs.
 8. A method comprising: in a block diagram edit-phase, propagating a signal label through navigable blocks.
 9. The method of claim 8 in which propagating is in response to a user request.
 10. The method of claim 8 in which propagating comprises displaying the propagated signal label on a graphical user interface (GUI).
 11. The method of claim 10 in which displaying comprises showing signal labels on implied signal connections on the GUI.
 12. The method of claim 8 in which propagating comprises providing an application program interface (API) for block in the block diagram model to specify how navigation occurs between inputs and outputs.
 13. The method of claim 12 in which the API further comprises specification of how navigation occurs between the outputs and the inputs.
 14. A method comprising: in a block diagram model, displaying an implied signal connection.
 15. The method of claim 14 in which displaying is in response to a user activating a hyperlink provided on a block that has an implicit signal connection with another block.
 16. The method of claim 14 in which displaying is in response to a user activating a hyperlink on a dialog of a block that has an implicit signal connection with another block.
 17. The method of claim 14 in which displaying comprises highlighting blocks involved in the implied signal connection.
 18. The method of claim 14 in which displaying comprises automatically drawing lines between blocks that have implied signal connections.
 19. A Graphical User Interface (GUI) for displaying results from a signal navigation comprises: a first element that defines a highlighting contrast value for determining a contrast between a highlighted portion and a remainder of a block diagram model; and a second element that highlights non-navigable source blocks and non-navigable destination blocks.
 20. The GUI of claim 19 in which the first element further comprises a command to enable a user to change the contrast.
 21. The GUI of claim 19 in which the first element further comprises a dialog box to enable a user to change the contrast.
 22. The GUI of claim 19 further comprising a third element that highlights an entire signal path from its non-navigable source to its non-navigable destination.
 23. The GUI of claim 22 further comprising a fourth element that fades a remainder of the block diagram model so that a highlighted portion is easily identified.
 24. The GUI of claim 23 further comprising a fifth element that enables a user to de-emphasize portions of the block diagram that are not highlighted. 